The present invention relates to a fluid level sensor and mount. More particularly, the present invention relates to a fluid level sensor that is insensitive to mineral deposits on the surface of the sensor, and a mount for the sensor.
One popular type of level sensor is a capacitive type of sensor. This sensor is used, for example, in automated machines, such as automated ice making machine. In a typical capacitive type sensor, a metal electrode in the shape of a rod is mounted vertically over a water reservoir. The reservoir is filled and emptied each machine cycle to reduce the build up of dissolved solids which can give the ice a cloudy appearance.
A small high frequency voltage is applied to the metal electrode, and when the water level in the reservoir makes contact with the rod, the capacitance of the rod to ground changes. This change is detected in a signal processing controller, and shuts off the pump filling the reservoir.
This type of sensor has at least one fundamental problem. It has been observed that when the electrode or rod becomes coated with a non-conducting material, such as a calcium carbonate mineral deposit, it acts as a dielectric, adding capacitance in series with the electrode. This additional capacitance is inversely proportional to the coating thickness. As such, as the coating builds up, the additional capacitance dominates the electrode capacitance to ground, at which point sensitivity to liquid level is lost.
In many systems, due to the monitoring and control systems, the loss of sensitivity to liquid level is not a fail safe event. For example in many automated ice making machines, if the water level cannot be detected, water will pump into the reservoir until an overload condition—based on timing—is detected and the pump is shut off. This can render the machine inoperable until service personnel remove the deposits or replace the rod. However, it has been found that cleaning can accelerate the rate of build up on rods.
Accordingly, there is a need for a fluid level sensor that is insensitive to mineral deposits on the surface of the sensor. Desirably, such a sensor is an acoustic-type sensor. More desirably, such a sensor can take various shapes and configurations and can be formed from different materials to suit a desired application. Most desirably, such a sensor is supported within a holder or support that readily accepts the sensor and that precludes the need to directly hard-wire any of the sensor components.